Tolerance and weed management systems in imidazolinone tolerant corn (Zea mays L.)

Abstract

Research was conducted to evaluate the efficacy of imidazolinone weed management systems and tolerance of imidazolinone tolerant corn to imazapic. Field experiments were conducted in 1997 and 1998 at the Texas Agricultural Experiment Station (TAES) Field Laboratory, near College Station TX, and at TP Farms, near Waller TX. Different imidazolinone herbicide treatments were applied to imidazolinone tolerant corn between the 2- to 3- and 6- to 8- leaf stage at 36 and 72 pa/ha to evaluate weed control, and 72, 105, 140, and 211 g/ha to evaluate the tolerance of imidazolinone tolerant corn. In 1997 at the TAES Field Laboratory control of Palmer amaranth, ivyleaf and entireleaf morningglory, Texas panicle, johnsongrass, common sunflower, and smellmelon were between 73 to 98% with imazapic or imazapyr plus imazethapyr, regardless of rate or application time. In 1998 at the TAES Field Laboratory control of devil's-claw, smellmelon, and johnsongrass ranged between 40 to 95% throughout the season with all imazapic applications. In 1997 at TP Farms near Waller TX effective control of Texas panicum and eclipse was obtained with all imazapic applications at 72 g/ha. Similar trends were observed with yellow nutsedge control. Due to the severe drought experienced in 1998, all weed species except for broadleaf signalgrass disappeared from the plots. Most effective control of yellow nutsedge, Texas panicle, spiny amaranth, and smellmelon occurred with early postemergence (EPOST) applications of imazapic (72 g/ha), while late postemergence (LPOST) applications of imazapic (72 g/ha) provided the highest control of broadleaf signalgrass. Similar herbicide tolerance was observed to both Gist varieties 8326IT and 8396IT. Crop response in these experiments refers to stunting and interveinal chlorosis. Increased crop response levels were observed early in the season, but by the end of the season had significantly decreased. In comparison, higher levels of crop response were observed in 1997 than in 1998, which can be attributed to the environmental conditions observed. Concerning crop height reductions, Gist variety 8326IT was shorter than 8396IT. No differences could be detected in the yields of either variety, when compared to the untreated check and other herbicide treatments.